Device for moving scattered X-ray diaphragms



July 27, 1954 w. KUHN ETAL 2,685,037

DEVICE FOR MOVING SCATTERED X-RAY DIAPHRAGMS Filed July 15, 1 952 //VlNTOR WERNER hu/m f/A/VSf/E/NR/CH VERSE By %/W Patented July 27, 1954'DEVICE FOR MOVING SCATTERED X-RAY DIAPHRAGMS Werner Kuhn,

Elmshorn, Verse, Hamburg-Fuhlsbuttel,

and Hansheinrich Germany, as-

signors to Hartford National Bank and Trust Company, Hartford, 001111.,as trustee Application July 15, 1952, Serial No. 298,888

Claims priority, application Germany November 2, 1951 Claims.

When making radiographs for medical examination, a screen retainingstray rays is arranged between the patient and the film in order toimprove the contrast. In order to prevent the raster structure of thisscreen from becoming visible on the radiograph, provisions are made tomove the screen during the exposure of the film.

If the screen is caused to perform a rocking movement by means of acrank rotating at constant speed, the speed characteristic of the screens substantially sinusoidal. with the aid of which the radiograph istaken is, moreover, fed by pulsatory current, it may occur that thescreen pattern is yet reproduced on the film, owing to a stroboscopiceffect which consists in that the shadow of the raster lamination isincident on the same lines in the plane of the film constantly at aninstant at which the intensity of the X-rays reaches a maximum value.The probability of this occurrence is the greatest some time before andafter the instant at which the speed of the screen movement has amaximum value, but also at certain accelerations stroboscopic effect mayoccur.

It should be noted that the raster may also be reproduced, not bystroboscopic effect, but by the fact that an instantaneous view is madeaccidentall at the instant at which the speed is zero.

Th invention provides a means to prevent the pattern of the stray-rayscreen from becoming visible on the radiograph owing to stroboscopiceffect.

According to the invention, with a device to cause the stray-ray screenin an X-ray apparatus to perform a rocking movement with a sinusoidal orsubstantially sinusoidal speed characteristic, a periodical movement inthe same direction, with higher frequency and preferably smalleramplitude is superimposed on the initial movement of the screen.

An excellently suitable solution of the problem in view is obtained, ifthe frequencies of the initial motion and that of the superimposedmotion are incommensurable relative to one another.

However, even if the frequency of the superimposed motion is a wholemultiple of that of the initial motion, an appreciable improvement isobtained, since even then the time intervals in which the speed maximaoccur and in which the speed varies little are replaced each by a seriesof intervals having great relative speed variations.

Thus the probability of disturbance owing to stroboscopic effect isreduced, since the reproduction of the screen pattern on the film ismade not by the simple occurrence of this effect, but

If the X-ray tube only if it also prevails long enough to permit theX-rays of producing a marked blackening of the film. If the timeintervals in which coincidence occurs are shortened strongly, theinter-- vals may be repeated more often without the occurrence of thestroboscopic effect.

The idea of the invention may be carried into effect in various ways.For example, the moving force may be supplied by two motors, of whichone supplies the initial movement, the other the superimposed movement,the two motors being connected with the screen via a differential gear.By using asynchronous motors in this manner or in a similar manner, thefrequencies of the initial movement and of the superimposed movement areincommensurable relative to one another. The two electric motors may, asan alternative, be replaced by a single motor which provides onemovement, for example, the initial movement of the screen, the othermovement being derived, for example, by means of planet gear from thefirst movement. In this case, it is true, the frequency of thesuperimposed movement is a whole multiple of that of the initialmovement, but this disadvantage will mostly be balanced by the advantageof more simple driving gear.

In order that the invention may be readily carried into effect, it willnow be described in detail with reference to the accompanying drawing.

Referring to the figure, reference numeral I designates a stray-rayscreen, which is connected with a connecting rod 2, which moves in theglide sleeves 3 and 4. With this rod is connected at point 5 a lever soas to be pivotable; by means of crank mechanisms known per se thedesired movements of the screen are given at the ends 1 and 8 of thislever. These movements, which have a sinusoidal or substantiallysinusoidal characteristic may be synchronous or asynchronous. Bychoosing the frequencies and the amplitudes of these componentmovements, the condition of movement provided by the superimposition maybe varied within Wide limits.

The use of the invention detracts by no means from the conditionsoccurring when the instant of a short exposure does not differ much fromthe instant at which the direction of the movement reverses. On thecontrary, owing to the superimposed movement even in this case thestatistic probability of a sufficient speed of the screen will begreater or the time during which the speed is so low that the screen issubstantially stationary, will be shorter.

What we claim is:

1. A device for rocking a stray-ray screen in an X-ray apparatuscomprising first means for imparting substantially sinusoidal periodicmovement to the stray-ray screen, and second means for imparting to saidscreen a periodic movement having a higher frequency and the samedirection as the initial movement imparted by said first means andsuperimposed thereon.

2. A device as claimed in claim 1 in which the superimposed movement hasa smaller amplitude than the initial movement.

3. A device as claimed in claim 1 in which the frequencies of theinitial movement and of the superimposed movement are incommensurablerelative to one another.

4. A device as claimed in claim 1, in which said first and second meanseach comprise a motor, and a differential gear connects the motor tosaid screen.

5. A device for rocking a stray-ray screen in References Cited in thefile of this patent UNITED STATES PATENTS Number Name Date 2,138,555Otvos Nov. 29, 1938 2,204,347 Files June 11, 1940 2,468,963 Dudley May3, 1949 2,554,051

Newton May 22, 1951

